1. Technical Field
The invention relates to a semiconductor device, and in particular, to a thyristor and its manufacturing method.
2. Description of Related Art
The thyristor is a semiconductor device used to protect the circuitry and might prevent the electronic components of the circuitry from interference or damage of the unexpected voltage surges. The voltage surges, for example, might be caused by the electrostatic discharge, lightning induction and induced voltage. Therefore, nowadays, thyristors are used in many electronic devices, like modems, universal serial buses (USBs), asymmetric digital subscriber lines (ADSLs), routers and set-top boxes, (STBs) and so on.
Some of electronic devices, such as the ADSL, the router, and the STB, have higher voltage sensitivity so that this kind of electronic devices are easily interfered and damaged by the voltage surges with a voltage value that is not relatively high. Thus, the thyristor which is utilized to protect this kind of electronic device usually need a lower breakdown voltage to avoid the interference or damage from the voltage surges.
The breakdown voltage of the thyristor is usually determined by the doping concentration of the base region. In general, the higher the doping concentration of the base region is, the lower the breakdown voltage of the thyristor is. In contrast, the lower the doping concentration of the base region is, the higher the breakdown voltage of the thyristor is. Therefore, the thyristors utilized in the above-mentioned electronic devices are made of the silicon substrate with a high doping concentration, so that the base region of this kind of thyristor usually has the higher doping concentration.